Cooperative Program on Clonal Eucalyptus Tolerance to the Hydrous and Thermal Stresses

Clonal plantations are the standard for fast-growing eucalyptus plantations, in both operational production areas, and in new afforestation areas. Experience from past rotation provides a basis for estimating risks and benefits of silvicultural decisions, but expanding afforestation in new frontiers poses higher risks of production due to environmental stresses different from those where the clones were selected.

Among the major environmental stresses to eucalyptus, two stand out because of their association with the new forest frontiers, namely: i) water stress (especially in regions of the midwest, north, northeast and the southeast of Brazil), and ii) the thermal stresses related to high temperatures (above 36º C) in tropical Brazil and low temperatures (below 5º C) in southern Brazil and Uruguay.

Even in traditional areas of planting, the effects of variation in water regime and heat due to climate change will require improved understanding of the sensitivity of clones to these stresses. Nutritional stress is also important in the productivity of eucalyptus plantations, but management options can easily mitigate this stress even in soils of low natural fertility.

Currently, the development of new clones is based on programs of controlled hybridization using parental material with suitable characteristics for growth, morphology, physiology, and biochemistry (overall “ecophysiology”) to tolerate environmental stresses through future rotations. Later selection focuses on individuals within these progenies that inherited a set of desired characteristics from their parents. This selection technique needs a great effort in terms of breeding, parental testing and field selection of potential materials for future clonal tests.

An alternative to this current methodology would be the possibility of "pre–select" the parents, or "pre–select" the progenies through molecular markers that are linked to desirable ecophysiological behaviors, such as rates of photosynthesis and respiration, patterns of root growth, stomatal response, carbon allocation, crown architecture, drought leaf senescence, tolerance to frost, cellular water potential, and other ecophysiological features. These different behaviors among individuals of Eucalyptus are commonly found in the field, either in tests of hybrid progenies or clonal tests.

The ecophysiological processes that lead to these observable responses of clones to drought and temperature extremes can be investigated through an experimental design that considers the interactions of stress agent, and variation of genetic material. These important responses include both traditional mensuration aspects (such as DBH and height), and also the fluxes of carbon, water and nutrients to provide ecophysiological insights into the mechanisms underlying wood production. Current technology and instrumentation allow us to examine how breeding can use physiological parameters to select more adapted clones.

TECHS Multidisciplinary

The TECHS program aims to use the knowledge gained from the BEPP and Eucflux (www.ipef.br/eucflux) research programs to develop powerful understandings of how the main environmental stresses to the Eucalyptus (hydric and thermal) interact with genetics. The results will have a wide application in forest management and breeding, including the effective ecophysiological modeling of clonal Eucalyptus at regional level and validation with environmental and genetic factors. These are also important goals for Promab (www.ipef.br/promab/), a watershed monitoring program focusing on micro-scale water requirements at the level of trees (clones) and stands as a basis for predicting changes in stream flow.

The TECHS Program can also include work conducted in other studies that examine networks of clonal tests across Brazil by characterizing some key ecophysiological behavior of the clones and broadening the teams of researchers (from physiology, hydrology, nutrition, breeding, biotechnology, entomology and plant pathology) engaged in these other networks. The advance to the next level of effective forest productivity should be linked to genetic-physiological understanding, regarding abiotic and biotic stresses.

Main TECHS issues

We need to identify which of ecophysiological mechanisms explain how different genetic materials can tolerate (and fail to tolerate) water stress, and to what extent these responses depend on thermal stresses. We also need to go beyond the range of the BEPP sites (tropical latitudes from 11º to 21º South) to test the effects of low temperatures on the production ecology of cold-stress areas.

TECHS will address five basic questions in order to estimate the productivity of future Eucalyptus plantations in traditional and newly afforested areas:

i) How is growth of clonal Eucalyptus plantations influenced by climate, in terms of ecophysiological responses of Leaf Area Index (light capture), light use efficiency, and the allocation of carbon (photosynthate)?
ii) How will clones interact with site and climatic factors, and to what extent can spacing influence these interactions?
iii) What are the ecophysiological mechanisms allow some clones to be better adapted to drought and heat stress?
iv) As the answers to these questions develop, it is possible to develop protocols capable of ecophysiologically classify a large number of individuals in breeding programs?
v) How the clones in different environments and under different stress levels, behave front of their susceptibility to pests and diseases (biotic stress)?

The TECHS program aims to answer these questions using a network of sites and clones, with manipulations of water regime and planting spacing. The TECHS network will have direct silvicultural uses in terms of assessing the climatic adaptability and susceptibility of key clones to biotic and abiotic stresses throughout Brazil.

The experimental design will enable breeders, biotechnologists, entomologists and plant pathologists to elucidate the tolerance mechanisms to drought and heat stress, as well as tolerance to pests and diseases, gene expression and its use in breeding programs. Foresters will be able to understand in more detail the interaction of plant spacing x genetic x site, through interactive effects on canopy closure, survival and final productivity, all of which will help tremendously in future decision making. In addition, monitoring the dynamics of LAI, for clone and site will enable to develop tools for monitoring the quality and health of plantations.

Finally, the project will also provide a set of information necessary to validateecophysiological models that can extrapolate information from studied clones and sites to other regions of the country.

The TECHS Project

The experimental design of the TECHS project uses the knowledge developed during 10 years of BEPP project and 4 years of Eucflux project, regarding installation, instrumentation and administration of experimental sites, as well as more than 15 years of studies with systematic spacing trials.

The TECHS design aims to “understand the variation of forest adaptability and productivity of a group of Eucalyptus clones across a wide range of edaphic-climatic conditions and stocking, and within each site, the responses to water deficit.”

The group of clones were be selected by forest breeders, the water regime will be manipulated by the technique of “rain exclusion”, and the stocking through the use of systematic planting design. The location of each site will be selected by each participating company to represent their region of interest.

TECHS design aims to “understand variation of the adaptabilityand productivityof a group of Eucalyptus clones across a wide edaphic-climatic and population density variation, and on each site, their responses to the hydric stress”.

General Genetic Material: a group of 18 Eucalyptus clones were selected by a group of breeders for planting in all TECHS sites. These clones will represent genetic materials currently in use in Brazil, but with distinct pedigree characteristics and susceptibility to hydric and thermal stresses. With this approach we are looking for different ecophysiological behaviors within adequate levels of productivity.

The 4 plastic clones will be general for all sites, while the remaining 7 clones will be specific for tropical (U or S) or subtropical (F). The TECHS will be working with 4 P + 3 U + 4 S + 7 F = 18 genetic materials, and that each site will have 11 genetic materials, with 4 general among all sites.

The list of the 18 TECHS clones, defined by the breeders of the forest companies, after long discussions and considerations about productivity, plasticity and phytosanitation.

For each genetic material, the designwill have one plot with regular rainfall,and another plot with rainfall exclusion to reduce water reaching the soil toabout 70% of actual rainfall (accomplished by covering 30% of the soil surface with roofs, Figure 1).Thus,each genetic material, at each sitewill be subject totwolevels water status. This approach avoids the expensive use of irrigation to evaluatethe effect of water, andrepresents more realistically the effects of droughts than could be done withirrigation.

In a contiguous area of the rain exclusion will installed a systematic design, so named because there is a continuous variation of the spacing between treatments. The design contains 12 plots, one for each genetic material, with 11 of the TECHS and 1 from the local company. Each plot contains 7 rows, 3 meters apart, with a variable distance between plants. The spacing represents a range from 476 to 13,333 trees per hectare, covering all the plausible range of commercial planting spacing. The systematic design does not need buffer areas between treatments, reducing planted area. In addition, studies with these designs showed that they are as effective as traditional block-planting designs to assess the effect of spacing on individual growth (m³ / tree) and total production (m³ / ha) of the stand.